1. Field of the Invention
The present invention relates to an analog-to-digital conversion system.
2. Description of the Related Art
Conversion of an analog value, for example, an analog voltage, to digital codes is usually performed in the field of measurements. In general, it is necessary that the requirements of the conversion method comprise such characteristics as a high conversion speed, high resolution, small power consumption, and small quantizing errors. A well known technique is that a cyclic analog-to-digital (A/D) conversion method is used in the analog-to-digital conversion circuit. This circuit is usually constituted by an integrated circuit (IC). In the conventional cyclic A/D conversion method, only one decision level voltage is applied to a comparator from an external circuit. An analog input voltage is sequentially compared with this decision level voltage, then code conversions are performed based on the generated digits obtained from resultant data of the comparison.
There are however, problems regarding the decision level voltage which is applied from the external circuit. That is, it is difficult to set the decision level voltage within the predetermined range of the offset value caused by, for example, characteristic fluctuations of circuit elements. The larger the offset value, the more errors in the generated digit. These problems will be explained in detail hereinafter.